Spitzer Space Telescope - General Observer Proposal #12028
The First Atmospheric Characterization of a Habitable-Zone Exoplanet
Principal Investigator: Kevin Stevenson
Institution: University of Chicago
Technical Contact: Kevin Stevenson, University of Chicago
Co-Investigators:
Jacob Bean, University of Chicago
David Charbonneau, Harvard University
Jean-Michel Desert, Univeristy of Colorado
Jonathan Fortney, UC Santa Cruz
Jonathan Irwin, Harvard University
Laura Kreidberg, University of Chicago
Michael Line, UC Santa Cruz
Ben Montet, Harvard University
Caroline Morley, UC Santa Cruz
Science Category: extrasolar planets
Observing Modes: IRAC Post-Cryo Mapping
Hours Approved: 8.3
Priority: 1
Abstract:
Exoplanet surveys have recently revealed nearby planets orbiting within stellar
habitable zones. This highly-anticipated breakthrough brings us one step closer
in our quest to identify cosmic biosignatures, the indicators of extrasolar
life. To achieve our goal, we must first study the atmospheres of these
temperate worlds to measure their compositions and determine the prevalence of
obscuring clouds. Using observations from the K2 mission, Co-I Montet recently
announced the discovery of a 2.2 Earth-radii planet within the habitable zone of
its relatively bright, nearby M dwarf parent star, K2-18. This temperate world
is currently the best habitable-zone target for atmospheric characterization.
Congruent with currently planned HST observations, we propose a Spitzer program
to measure the transmission spectrum of the first habitable-zone exoplanet.
Both telescopes are essential to revealing K2-18b's chemical composition. In a
cloud-free, hydrogen-dominated atmosphere, the precision achieved by these
measurements will be sufficient to detect methane, ammonia, and water vapor,
which are the dominant C, N, and O bearing species at these temperatures. In
turn, elemental abundance constraints from a primordial atmosphere can tell us
about the composition of a protoplanetary disk in which Earth-like planets could
have formed. Conversely, if the atmosphere contains thick clouds then the
multi-wavelength observations from K2, HST, and Spitzer will constrain the
clouds' properties. Because temperature plays a key role in the formation of
clouds, their detection within the atmosphere of this habitable-zone exoplanet
would be an important signpost that serves as a guide to future investigations
of smaller, rocky exoplanets. As K2 continues discovering more habitable-zone
planets, it is imperative that we perform spectral reconnaissance with Spitzer
to determine their physical characteristics and begin understanding the
prevalence of potentially-obscuring clouds prior to the launch of JWST.